Third seed Zheng Saisai comfortably accounted for countrywoman Zhu Lin to reach the quarter-finals of the Monterrey Open on Thursday.

Zheng, who is ranked 27th in the world, triumphed 6-1 6-2 in a dominant display where she was seldom challenged.

In the last eight, Zheng will face eighth seed Ann Li, who overcame Slovenian Tamara Zidansek 6-4 6-3 at the WTA International tournament.

Zheng is the highest remaining seed left standing in the draw after the first-round exits of top seed Sloane Stephens and Nadia Podoroska.

Russian qualifier Anna Kalinskaya continued her good run with a 6-4 6-3 victory over Nina Stojanovic and she will next face Viktorija Golubic in the quarters – the latter topped Lauren Davis 6-3 6-1.

A record seven Russians will contest the quarter-finals of the St Petersburg Ladies Trophy after victories for seeds Veronika Kudermetova and Daria Kasatkina on Thursday.

Number two seed Kudermetova edged past Kamilla Rakhimova 7-5 3-6 7-6 (7-5), while eighth seed Kasatkina also needed three sets to see off Aliaksandra Sasnovich 5-7 6-3 7-6 (7-2). 

Wildcard Margarita Gasparyan held off Katerina Siniakova 6-4 6-4 and qualifier Anastasia Gasanova shocked fifth seed Anastasia Pavlyuchenkova 1-6 7-6 (10-8) 7-6 (7-4). 

They joined fellow Russians Vera Zvonareva, Ekaterina Alexandrova and Svetlana Kuznetsova in the last eight, with Romanian qualifier Jaqueline Cristian also in the line-up.

The previous highest number of Russians in a WTA quarter-final line-up was six, set at Moscow 2005 when Kuznetsova was joined by Dinara Safina, Elena Dementieva, Maria Sharapova, Anastasia Myskina and Elena Likhovtseva.

The last time a single nation had as many players at this stage of a WTA event was in Oakland in 1993 when the United States produced seven of the eight quarter-finalists.

Denis Shapovalov secured a straight-sets win over Jeremy Chardy to set up a semi-final showdown with qualifier Lloyd Harris at the Dubai Tennis Championships. 

The third seed struck 26 winners en route to a 7-5 6-4 triumph on Thursday, but it was his serve that pleased him most.

Shapovalov, ranked 12th in the world, sent down 10 aces as Frenchman Chardy was deprived of any break-point openings.

"I've focused on my serve a lot in the past couple of weeks," the Canadian said.

"I have worked on placing it and tried out different types of serves to have more variation. I hope I can continue that.

"I've also worked on my footwork and positioning during rallies. I am feeling the ball well on both sides. If I am moving well, everything goes into place."

Harris was a surprise winner over Kei Nishikori, sealing a 6-1 3-6 6-3 success to dump out the former world number four.

Second seed Andrey Rublev defeated Marton Fucsovics 7-5 6-2 and will now face fellow Russian Aslan Karatsev.

Wildcard Karatsev continued his run with a hard-fought victory over teenager Jannik Sinner, coming from a set down in a 6-7 (5-7) 6-3 6-2 win.

Top seed Stefanos Tsitsipas and fellow star Alexander Zverev progressed to the Mexican Open quarter-finals on Wednesday, but Milos Raonic bowed out.

Tsitsipas was too good for big-serving American John Isner in a 6-3 6-2 victory in Acapulco midweek.

A two-time Australian Open finalist, having also reached the French Open final four last year, Tsitsipas excelled on serve against Isner.

Greek star Tsitsipas only dropped one point on his first serve – not facing a break point throughout the last-16 contest – while firing down eight aces.

Standing in the way of Tsitsipas and a semi-final spot at the ATP 500 tournament is Canadian sensation Felix Auger-Aliassime.

In a battle of the NextGen, seventh seed Auger-Aliassime saved four of five break points in a 6-3 6-4 win over wild card Sebastian Korda.

Zverev will feature in his third Mexican Open quarter-final in four years after the second seed took down Laslo Djere 6-4 6-3.

Runner-up in 2019, Zverev will next face eighth seed Casper Ruud – who topped Tallon Griekspoor 4-6 6-3 7-6 (7-3) in the quarters.

"I think today what showed the most is that I got better with the match," Zverev said. "I started off extremely sloppy, started off with a lot of unforced errors.

"The longer the match went on the better I started playing and this is something that is very important for me. When I get into a rhythm I feel very comfortable on court and that's how I felt today."

Elsewhere, Lorenzo Musetti's giant-slaying run continued following a 2-6 6-3 7-6 (7-1) victory against Frances Tiafoe.

Musetti earned his first ATP 500 quarter-final as the Italian prepares to meet fifth seed Grigor Dimitrov, who eased past Miomir Kecmanovic 6-4 6-2.

There was an upset after fourth seed Raonic crashed out 6-4 6-2 at the hands of Dominik Koepfer, while sixth seed Fabio Fognini lost 6-4 6-3 against Cameron Norrie.

Canadian teenager Leylah Fernandez booked her spot in the Monterrey Open quarter-finals after easing past Kristina Kucova.

Fernandez cruised into the last eight of the WTA International tournament on Wednesday by defeating Slovakia's Kucova 6-1 6-4 in Mexico.

Kucova had eliminated top seed and 2017 US Open champion Sloane Stephens on Tuesday, but she was no match for the 18-year-old Fernandez midweek.

Next up for Fernandez is Viktoria Kuzmova, who beat lucky loser Harriet Dart 6-4 6-3.

Spanish seventh seed Sara Sorribes Tormo did not have to take to the court, benefiting from a walkover after Kaja Juvan withdrew.

Sorribes Tormo will face Anna Karolina Schmiedlova, who outlasted Jasmine Paolini 2-6 6-2 6-2.

Russian duo Svetlana Kuznetsova and Vera Zvonareva recorded contrasting victories on home soil to reach the last eight of the St. Petersburg Ladies Trophy.  

Kuznetsova - who has won both the French and US Open during her distinguished career - needed just over an hour to get past teenage qualifier Wang Xinyu by a 6-1 7-5 scoreline.  

The 35-year-old converted six of the nine break-point opportunities she created, though was made to work for her win in the second set having previously taken nine of the opening 10 games.  

After failing to serve out for the match when 5-3 ahead, the fourth seed eventually prevailed when recording a break of her own with the score at 6-5.  

Zvonareva, meanwhile, was on court for three hours and 10 minutes as she produced an impressive upset, knocking out third seed Fiona Ferro 6-7 (8-6) 7-5 7-6 (7-2).  

"We both were fighting for every point, trying to hang in there. I think I was able to play some good tennis when it mattered, and I'm happy with the win of course,” Zvonareva said after being involved in the longest match in the history of the tournament, per the WTA's website.  

The 36-year-old came out on top in a deciding tie-break having been unable to hold on to an early 2-0 lead in the set.  

Anastasia Gasanova and Katarina Zavatska had set a new record for the longest contest earlier on Wednesday, the former eventually prevailing 6-2 6-7 (8-6), 7-5 after three hours and four minutes in an eventful first-round tie.

Ekaterina Alexandrova is another Russian player to progress to the last eight, seeing off Tereza Martincova in straight sets.

In the final match, Romanian qualifier Jaqueline Cristian surprised Jelena Ostapenko 6-3 7-6 (11-9) to reach her first ever WTA 500 quarter-final, where her opponent will be Kuznetsova.

Jannik Sinner fought hard to earn an impressive victory that knocked fourth seed Roberto Bautista Agut out of the Dubai Tennis Championships. 

The 19-year-old rising star, who won the Great Ocean Road Open last month, prevailed in a match that remained in the balance until the end on Wednesday. 

Sinner won 6-4 3-6 7-5 to reach the quarter-finals, with Bautista Agut following top seed Dominic Thiem - who lost in the second round - out of the tournament. 

After hitting 16 aces, Sinner – the youngest player in the ATP Tour top 100 – will face surprise Australian Open semi-finalist Aslan Karatsev next. 

Second seed Andrey Rublev is through after a comfortable 6-3 6-1 win over Taylor Fritz. 

Rublev will face Marton Fucsovics, who ousted Serbian Dusan Lajovic in three sets, in the last eight. 

The Russian now has 22 consecutive wins at ATP 500 events, a run that has included four titles at that level. Only Roger Federer has ever recorded a longer streak, doing so with a run of 28 between 2014 and 2016.

"I am really happy that I can win in straight sets and quite confidently," Rublev said. 

"I know Taylor since [the] juniors and it is always tough to play against him, because he has a huge serve and he is playing really fast. 

"The first set was not even rallies because everything was serve, winner or serve, mistake, so everything was so fast. 

"In these conditions, it is tough to find the rhythm. You don't know what's going to happen and it's really not easy, but I'm happy that in the end I made it."

Third seed Denis Shapovalov is also through after a 6-4 6-3 win over Hubert Hurkacz, the Canadian booking a last-eight meeting with Jeremy Chardy. 

Kei Nishikori will play Lloyd Harris in the other quarter-final. 

Italian qualifier Lorenzo Musetti may be ranked 120th in the world but he claimed his maiden top-10 scalp on Tuesday, beating Diego Schwartzman in the first round of the Mexican Open.

Musetti, the Australian Open boys' singles champion in 2019, secured a 6-3 2-6 6-4 win over ninth-ranked Schwartzman in a stunning success.

"There is a lot of work, a lot of sacrifice and I think some tears left in my eyes," the 19-year-old said during his on-court interview.

"I'm really proud of myself, but now I'm going to work harder and focus on the next days."

Musetti, whose forehand was excellent, defeated both Stan Wawrinka and Kei Nishikori at the Internazionali d'Italia in Rome last year.

Top seed Stefanos Tsitsipas had no such trouble, easing into the second round, where he will face big-serving American John Isner.

The Greek world number five beat France's Benoit Paire 6-3 6-1, aided by a strong display on serve.

"I didn't know what to expect from Benoit today," Tsitsipas said. "I think it's kind of tricky playing a tournament you haven't played before."

On facing 27th-ranked Isner next up, Tsitsipas added: "He's a guy that serves really well so that's going to be the biggest element and the one thing that I'll really have to resolve during that match."

Fourth seed Milos Raonic sent down 13 aces as he defeated American Tommy Paul 7-6 (8-6) 6-4.

In the late match, fifth seed Grigor Dimitrov got past Adrian Mannarino, who retired when trailing 6-4 3-0.

Former US Open champion Sloane Stephens has continued her torrid start to 2021 after crashing out in the first round of the Monterrey Open on Tuesday.

Stephens went into the Mexico event as top seed but lost to Slovakian world number 151 Kristina Kucova 6-2 6-2.

The 27-year-old American is now 0-4 to start the 2021 WTA Tour season and has won only one set all season.

Stephens, now ranked 48th in the world, only managed to win 32.4 per cent of points on her first serve, with Kucova converting seven of 14 break points in the match.

Second seed Nadia Podoroska was also a first-round casualty on Tuesday, going down 6-4 6-4 to Russian qualifier Anna Kalinskaya.

In the late match, Eugenie Bouchard went down to China's Lin Zhu 7-5 7-6 (6-3).

Top seed Dominic Thiem was beaten in straight sets in the second round of the Dubai Tennis Championships by Lloyd Harris.

The reigning US Open champion, given a bye for the first round, lost 6-3 6-4 to his South African opponent, who sits 77 places further down the ATP rankings.

The Austrian has endured a difficult start to 2021. He lost in straight sets to Grigor Dimitrov in the last 16 of the Australian Open and was beaten by Roberto Bautista Agut in the quarter-finals in Doha.

It was a first win over a top-five player for Harris, who was not once taken to deuce on serve during their 72 minutes on court.

"I'm super, super happy with that win. [He is] by far the highest-ranked player I have beat," said Harris. "I look up to Domi a lot so, for me, it is a special feeling. I am really happy. Just the fact that I am playing good tennis, match in, match out now is giving me a lot of confidence.

"I was serving really well. I don't think I faced any break points. I took control of those games and [in] one or two games on his serve, I gave myself a good look. I played some of the important points very well. I am very proud of that."

While Thiem is struggling for form, things are looking far better for Andrey Rublev, who beat Emil Ruusuvuori 6-4 6-4 to stretch his winning streak at ATP 500 events to 21 matches.

The world number eight, who will face Taylor Fritz in the next round, equalled Andy Murray for the second-best winning run at this level of the Tour. Roger Federer (28) holds the record.

Third seed Denis Shapovalov beat Jan-Lennard Struff for the loss of just four games, while Bautista-Agut advanced after opponent Matthew Ebden retired in the first set.

Fifth seed David Goffin was beaten in straight sets by Kei Nishikori, who recorded just his third victory of the year.

Karen Khachanov and Jannik Sinner each advanced after three-setters, while Marton Fucsovics and Aslan Karatsev were also taken the distance before progressing.

Hubert Hurkacz, Lorenzo Sonego, Dusan Lajovic, Aljaz Bedene and Filip Krajinovic also won on Tuesday.

Daria Kasatkina fended off fast-rising star Clara Tauson at the St Petersburg Ladies Trophy as the Russian home favourite edged a clash of recent tournament winners.

Former world number 10 Kasatkina, who landed the Phillip Island Trophy title in Melbourne last month, came through a roller coaster second set against the qualifier to tie up a 6-4 7-6 (7-0) first-round victory.

Former junior world number one Tauson won the Lyon Open at the start of March, and the 18-year-old Danish player twice broke when Kasatkina was serving for the match to take their tussle to a tie-break that was then unexpectedly one-sided.

Having been jittery when serving at 5-4 and 6-5, Kasatkina found composure when it mattered to see out the match.

Tauson had won 13 consecutive matches, including qualifiers, and had reeled off 20 successive sets during that run, but Kasatkina interrupted the hot streak.

Three-time WTA tournament winner Kasatkina, seeded eighth this week, said on Amazon Prime: "You're right, I was nervous serving for the match, but I'm glad I could close out the match playing the tie-breaker.

"Sure, there is something to improve, but I don't want to talk about it right now. I'm going to talk to my coach about what I need to improve. She wasn't an easy opponent. She just won a tournament and I knew it was going to be a tough match, and a tough match it was."

Two 19-year-old qualifiers were also among Tuesday's winners, as Chinese player Wang Xinyu and Russian Kamilla Rakhimova safely went through to the last-16 stage.

Rafael Nadal has withdrawn from the Miami Open as he bids to recover full fitness in time for the European clay season.

The 20-time grand slam singles champion has not played since losing to Stefanos Tsitsipas in the quarter-finals of the Australian Open in February.

Nadal pulled out of the Rotterdam Open and turned down a wildcard for the Dubai Tennis Championships due to a persistent back problem.

The world number three, who has never won the title in Miami, wants to prioritise his recovery ahead of the beginning of the clay-court swing in April.

Writing on Twitter on Tuesday, he said: "Sad to announce that I won't be playing in Miami, a city that I love.

"I need to fully recover and get ready for the clay-court season in Europe. Special message to my fans in the US and in particular to the great Spanish-speaking community FL who always give me a great support!"

Nadal follows long-time rival Roger Federer in withdrawing from the tournament, the Swiss great choosing to focus on training after only returning to the Tour from a 14-month absence at the Qatar Open.

Federer is the reigning champion in Miami, having beaten 2018 winner John Isner in the final two years ago. The 2020 tournament was cancelled due to coronavirus concerns.

Alexander Zverev cruised into the second round of the Mexican Open as debutant Sebastian Korda enjoyed a memorable debut in Acapulco.

German star and second seed Zverev accounted for teenager Carlos Alcaraz, the 2019 runner-up winning the opening-round clash 6-3 6-1 on Monday.

Alcaraz – in his first showdown against a top-10 player – broke for a 2-0 lead and while he continued to go toe-to-toe with Zverev through six games, the 17-year-old was unable to maintain his charge.

Zverev broke for a 4-3 lead and the 2020 US Open finalist did not look back, winning nine of the last 10 games to advance in 84 minutes.

"He started off playing extremely well, he didn't miss a lot of balls. Then I felt more comfortable on court, this is the first round," Zverev said.

"It's not always easy to play a first round, especially against a player like this, who is very young, who is very motivated and who wants to compete. I'm actually quite happy with how the match went."

Next up for Zverev – who reached the Australian Open quarter-finals in February – is Serbia's Laslo Djere.

Djere took down Steve Johnson 6-2 6-3 for a spot in the last 16.

Meanwhile, Korda capped his Acapulco bow with a shock 7-5 6-2 win against former world number three Marin Cilic.

Korda claimed his first ATP 500-level victory having saved 10 of the 11 break points he faced in the opening set against the 2014 US Open champion.

Canadian sensation and seventh seed Felix Auger-Aliassime awaits after the 20-year-old converted his sixth match point to see off Tennys Sandgren 6-3 7-6 (10-8).

Elsewhere, John Isner and Dominik Koepfer also advanced.

Nao Hibino was a shock first-round casualty at the Monterrey Open, while fellow seed Ann Li advanced.

Seeded ninth for the WTA International tournament, Japan's Hibino was upstaged 3-6 6-2 6-3 by Jasmine Paolini on Monday.

American eighth seed Li, however, had no such trouble in her 6-3 7-5 victory over Arantxa Rus on the outdoor hard courts.

Coco Vandeweghe – the 2017 Australian Open semi-finalist – suffered another early exit in Mexico.

After being ousted by Mihaela Buzarnescu in the opening round in Guadalajara last week, former world number nine Vandeweghe was eliminated 6-3 6-2 by Canadian teenager Leylah Fernandez.

Fernandez will face either top seed Sloane Stephens or lucky loser Kristina Kucova in the second round.

Anna Karolina Schmiedlova, Nina Stojanovic, Viktoria Kuzmova, Lauren Davis and Tamara Zidansek also progressed from the opening round.

Former world number one Andy Murray will compete at the Miami Open for the first time since 2016 after being granted a wildcard.

Murray has not played on the ATP Tour since last month's Rotterdam Open, where the three-time major champion lost to Andrey Rublev in the round of 16.

But Murray – who won the ATP 1000 event in 2009 and 2013 – is set to end his Miami absence, having undergone hip surgeries in 2018 and 2019.

"It's a city I love, and I've spent a lot of time here over the last 15 years, I feel comfortable," the 33-year-old, who sat out the Australian Open after testing positive for coronavirus, told PEOPLE Magazine.

"But over the next few months, I want to play matches — especially against the top players — work on my game and climb the rankings. I want to get back playing a sport I love."

Murray added: "The last few years has been really hard. After the operation, there were no guarantees I would play again, but I've been working very hard on my conditioning and over the last few months I've felt the best I have for years. 

"I'll need to be mindful of my schedule moving forward but I'm excited to be back competing — with a metal hip."

"But every match feels like progress and I'm learning from each one," he continued.

The Miami Open will get underway at Hard Rock Stadium on March 24 after the tournament was cancelled last year amid the COVID-19 pandemic.

"It is exciting to see Andy back in Miami," Miami Open Tournament Director James Blake said.

"As someone who has had to battle back from injuy during his career, I understand and respect all the hard work Andy has put in to get back on tour."